<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .nav {
            background-color: black;
            color: white;
        }

        .nav a:link {
            color: white;
            text-decoration: none;
        }
        .nav a:hover {
            color: white;
            text-decoration: underline;

        }
        .nav a:visited {
            color: white;
        }
        .nav a:active {
            color: white;
        }

        .main {
            background-color: blue;
        }
        a.white {
            color: white;
        }
        
        a.white:link {
            color: white;
        }
        a.white:hover {
            color: red;
        }
        a.white:visited {
            color: white;
        }
        a.white:active {
            color: white;
        }

        a.red:link {
            color: red;
        }
        a.red:hover {
            color: red;
        }
        a.red:visited {
            color: red;
        }
        a.red:active {
            color: red;
        }
        .b {
            font-weight: bold;
        }
    </style>
</head>
<body>
<div class="nav">
        aaaa
    <a href="http://www.xxxxyyyy.com">百度</a>
    <a href="http://www.xxxxyyyy.com">百度</a>
    <a href="http://www.xxxxyyyy.com">百度</a>
    <a href="http://www.xxxxyyyy.com">百度</a>
</div>
<div class="main">
    <a href="http://www.xxxxyyyy.com" class="white">百度</a>
    <a href="http://www.xxxxyyyy.com" class="white">百度</a>
    <a href="http://www.xxxxyyyy.com" class="white">百度</a>
    <a href="http://www.xxxxyyyy.com" class="white">百度</a>
</div>
<div>

    <a href="http://www.xxxxyyyy.com">百度</a>
    <a href="http://www.xxxxyyyy.com" class="red b">百度</a>
    <a href="http://www.xxxxyyyy.com" class="b">百度</a>
    <a href="http://www.xxxxyyyy.com">百度</a>
</div>
</body>
</html>